Butene-1 copolymer and resin composition containing the same

ABSTRACT

Copolymers of butene-1 and propylene, having specific physical properties and substantially a syndiotactic structure; and easily heat-sealable polypropylene resin compositions comprising 5-50 parts by weight of one of the copolymers and 95-50 parts by weight of a stereoregular crystalline propylene-ethylene copolymer or propylene-ethylene-C 4-12  -α-olefin copolymer having specific compositions and melt flow index.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The present invention relate to copolymers of butene-1 and propylene andalso to heat-sealable polypropylene resin compositions containing one ormore of the copolymers and useful as heat-sealing layers forheat-bonding polyolefins.

b) Description of the Related Art

The existence of α-olefin polymers having a syndiotactic structure hasbeen known for many years, including syndiotactic polypropylene by wayof example. Syndiotactic polypropylene can be obtained by conductingpolymerization at a low temperature in the presence a conventionalcatalyst composed of a vanadium compound, ether and an organoaluminumcompound. This polypropylene however has poor syndiotacticity so that itcan hardly be considered to have the properties of a syndiotacticpolypropylene.

J. A. Ewen et al. has found for the first time that polypropylene havingsuch good tacticity as exceeding 0.8 in terms of syndiotactic pentadfraction as measured by ¹³ C-NMR can be obtained by polymerizingpropylene in the presence of a polymerization catalyst composed ofmethyl aluminoxane and a transition metal (Hf and Zr) compound having anasymmetric ligand (J. Amer. Chem. Soc., 110, 6255-6, 1988).

In the meantime, it has been found by the present inventors thatpolybutene-1 having high syndiotacticity can be obtained when butene-1is polymerized using the above catalyst in a high-purity form. Thiscatalyst has good activity per transition metal and, moreover, theresultant polybutene-1 has high tacticity. However, the balancing ofphysical properties of the polybutene-1 is rather poor and articlesmolded from the polybutene-1 have insufficient transparency.

Polypropylene resins which substantially have stereoregularity, namely,either an isotactic structure or a syndiotactic structure have excellentstiffness and are superior in external appearance such as transparencyand gloss. They are hence used for various applications. For films,propylene-ethylene copolymers are used to improve impact resistance andheat sealability. As resins having excellent balance among stiffness,impact resistance and heat sealability, propylene-ethylene-butene-1terpolymers are known by way of example.

Although these copolymers have excellent balance among stiffness, impactresistance and heat sealability, it is desired to improve the heatsealability further so that the efficiency in the use of films can beimproved.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a copolymer of butene-1and propylene, which has excellent impact resistance and goodtransparency and substantially has a syndiotactic structure.

Another object of the present invention is to provide a heat-sealablepolypropylene resin composition excellent not only in heat sealabilitybut also in other physical properties.

Other objects will become apparent from the following description of thepresent invention.

In one aspect of the present invention, there is provided a copolymer ofbutene-1 and propylene, wherein, of an absorption of the side-chainmethylene groups of butene-1 units of said copolymer as measured in theform of a 1,2,4-trichlorobenzene solution by ¹³ C-NMR, the intensity ofan absorption observed at about 26.9 ppm using tetramethylsilane as astandard is at least 0.3 of the intensity of a full absorption of theside-chain methylene groups observed at about 27.8-26.0 ppm usingtetramethylsilane as a standard; the content of propylene units rangesfrom 0.1 wt.% to 20 wt.%; and the intrinsic viscosity as measured at135° C. in the form of a tetralin solution is at least 0.05.

In another aspect of the present invention, there is also provided aheat-sealable polypropylene resin composition comprising 95-50 parts byweight of substantially stereoregular crystalline polypropylene composedof 98-80 wt.% of propylene units, 0-18 wt.% of α-olefin units having4-12 carbon atoms and 2-20 wt.% of ethylene units and a melt flow indexof 0.1-100 g/10 min as measured at 230° C.; and 5-50 parts by weight ofthe above butene-1-propylene copolymer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The butene-1-propylene copolymer of the present invention, whichsubstantially has a syndiotactic structure, can be obtained bycopolymerizing butene-1 and propylene in the presence of a catalyst.Although the compounds disclosed in the literature by J. A. Ewen et al.can be mentioned as exemplary polymerization catalysts, other catalystsystems can also be used even when they have a different structure, aslong as they can afford propylene butene-1 homopolymer having relativelyhigh tacticity of at least 0.5 or so in terms of syndiotactic pentadfraction [A. Zambelli et al.: Macromolecules, 6, 925 (1973); ibid., 8,687 (1975)]. For example, catalyst systems formed of an aluminoxane anda transition metal compound having an asymmetric ligand are effective.

Illustrative transition metal compounds suitable for the production ofthe copolymers of the present invention includeisopropyl(cyclopentadienyl-1-fluorenyl)hafnium dichloride andisopropyl(cyclopentadienyl-1-fluorenyl)zirconium dichloride described inthe above publications as well as those obtained by substituting one orboth of their chlorine atoms with the corresponding number of otherhalogen atoms or C₁₋₅ -alkyl groups.

Exemplary aluminoxanes include the compounds represented by thefollowing formula: ##STR1## wherein R is a hydrocarbon residual grouphaving 1-3 carbon atoms. Especially, methylaluminoxanes of the aboveformula in which R is a methyl group and n is at least 5, preferably 10or greater are used.

The aluminoxane can be used in a proportion of 10-1,000,000 molar times,usually 50-5,000 molar times the transition metal compound.

No particular limitation is imposed on the polymerization conditions.The polymerization can be conducted by polymerization in the presence ofan inert solvent, by bulk polymerization in a polymerization systemsubstantially free of inert solvent, or by vapor-phase polymerization.Generally, the polymerization temperature may range from -100° C. to200° C. and the polymerization pressure from normal pressure to 100kg/cm² -G. Polymerization at -100° C. to 100° C. and normal pressure to50 kg/cm² -G is particularly preferred.

Upon polymerization, it is important to control the feed rate of eachmonomer into a polymerization system so that the content of propyleneunits in the resulting copolymer can be 0.1-20 wt.%, preferably 1-20wt.%. It is also important to control the feed ratio of the monomers,the polymerization temperature and the like so that, of an absorption ofthe side-chain methylene groups of butene-1 units of said copolymer asmeasured in the form of a 1,2,4-trichlorobenzene solution by ¹³ C-NMR,the intensity of an absorption observed at about 26.9 ppm usingtetramethylsilane as a standard is at least 0.3, preferably at least 0.4of the intensity of a full absorption of the side-chain methylene groupsobserved at about 27.8-26.0 ppm using tetramethylsilane as a standard;the content of propylene units ranges from 0 1 wt.% to 20 wt.%; and theintrinsic viscosity as measured at 135° C. in the form of a tetralinsolution is at least 0.05. Further, it is desirable to treat theresultant copolymer, for example, by washing it with a solvent such as aC₃₋₂₀ hydrocarbon. Usable exemplary hydrocarbon solvents includepropylene itself; saturated aliphatic hydrocarbons such as propane,butane, pentane, hexane, heptane, octane and nonane; aromatichydrocarbons such as benzene, toluene, xylene and ethylbenzene; andthose obtained by either partially or wholly substituting the hydrogenatoms of such saturated aliphatic hydrocarbons or aromatic hydrocarbonswith fluorine, chlorine, bromine and/or iodine atoms. Other exemplaryusable solvents include low molecular-weight compounds capable of eitherdissolving or dispersing the atactic component, such as C₁₋₂₀ alcohols,C₂₋₂₀ ethers and esters. No particular limitation is imposed on thewashing method. Generally, the washing can be conducted at 0°-100° C.

Polymerization at a relatively low temperature, usually at 100° C. orlower in the presence of a catalyst having high purity, normally of 90%or higher is also effective for obtaining the above copolymer.

In the butene-1-propylene copolymer of the present invention, thecontinuous chain of butene-1 units substantially has a syndiotacticstructure. This copolymer is defined as follows. Namely, of anabsorption of side-chain methylene groups of butene-1 units of thecopolymer as measured in the form of a 1,2,4-trichlorobenzene solutionby ¹³ C-NMR, the intensity of an absorption observed at about 26.9 ppmusing tetramethylsilane as a standard is at least 0.3 of the intensityof a full absorption of the side-chain methylene groups observed atabout 27.8-26.0 ppm using tetramethylsilane as a standard, the contentof propylene units ranges from 0.1 wt.% to 20 wt.%, and the intrinsicviscosity as measured at 135° C. in the form of a tetralin solution isat least 0.05. If the parameter specified as an index forsyndiotacticity on the basis of the results of ¹³ C-NMR measurement issmaller than 0.3, the balancing of physical properties will becomepoorer. Intrinsic viscosities lower than 0.05 will result incompositions having inferior physical properties, especially will leadto poor anti-blocking property when formed into films. Such lowintrinsic viscosities are therefore not preferred. The upper limit ofthe intrinsic viscosity may be 5 or so. Propylene unit contents lowerthan 0.1 wt.% will be too little to significantly improve thetransparency of the polymer, whereas propylene unit contents higher than20 wt.% will lead to insufficient stiffness. The number-averagemolecular weight as measured by gel permeation chromatography inpropylene can preferably be at least 1,000, especially 5,000 or higher.The ratio of the weight-average molecular weight to the number-averagemolecular weight (hereinafter abbreviated as "Mw/Mn") can preferably be1.5-10.

The substantially stereoregular crystalline polypropylene employed as acomponent in the polypropylene resin composition of the presentinvention may be either polypropylene of substantially an isotacticstructure or polypropylene of substantially a syndiotactic structure.The crystalline polypropylene contains 98-80 wt.% of propylene units,0-18 wt.% of α-olefin units and 2-20 wt.% of ethylene units and has amelt flow index of 0.1-100 g/10 min as measured at 230° C.

The term "polypropylene of substantially an isotactic structure" meanspolypropylene which shows at about 21.4 ppm an absorption attributedprincipally to the methyl groups of propylene units on a ¹³ C-NMRspectrum, while the term "polypropylene of substantially a syndiotacticstructure" means polypropylene which presents the above absorption at20.2 ppm.

Polypropylene substantially having an isotactic structure can beproduced by a process well known in the art, for example, bypolymerizing propylene and ethylene and, if desired, a C₄₋₁₂ α-olefin inthe presence of a catalyst, which is formed of titanium trichloride orits modified product or titanium tetrachloride supported together withan electrondonating compound on a carrier such as magnesium chloride, incombination with an organoaluminum compound and, if necessary, anelectron-donating compound. Various commercial products are available assuch polypropylene.

On the other hand, polypropylene substantially having a syndiotacticstructure can be produced by polymerizing propylene and ethylene and, ifdesired, a C₄₋₁₂ α-olefin in the presence of a similar catalyst undersimilar polymerization conditions to those employed in thecopolymerization of butene-1 and propylene.

The substantially stereoregular polypropylene must contain 98-80 wt.% ofpropylene units, 0-18 wt.% of C₄₋₁₂ α-olefin units and 2-20 wt.% ofethylene units. Propylene unit contents lower than 80 wt.% will resultin formed articles having poor stiffness. On the other hand, propyleneunit contents higher than 98 wt.% will lead to formed articles havingpoor impact resistance. C₄₋₁₂ α-olefin unit contents higher than 18 wt.%will result in formed articles having poor stiffness. Ethylene unitcontents lower than 2 wt.% will lead to poor impact resistance and heatsealability, while ethylene unit contents higher than 20 wt.% willresult in formed articles having poor stiffness. Further, from thestandpoint of moldability, the melt flow index as measured at 230° C.must be 0.1-100 g/10 min. Formation into films will become difficult ifthe melt flow index is outside the above range, no matter whether it issmaller than 0.1 g/10 min or greater than 100 g/10 min.

The preferable ranges of the respective units in the substantiallystereoregular crystalline polypropylene are 97-85 wt.% for the propyleneunits, 0-15 wt.% for the C₄₋₁₂ α-olefin units, and 3-15 wt.% for theethylene units. The preferable range of the melt flow index is 1-50 g/10min.

Regarding the blending proportions of the substantially stereoregularcrystalline polypropylene and the butene-1-propylene copolymer of asubstantially syndiotactic structure, it is necessary to blend 95-50parts by weight of the former resin with 5-50 parts by weight of thelatter resin. If the proportion of the former resin is greater than 95parts by weight, no significant effects will be exhibited for theimprovement in heat sealability. Proportions smaller than 50 parts byweight will result in poor physical properties such as poor stiffnessand anti-blocking property. The preferable blending proportions are90-60 parts by weight for the substantially stereoregular crystallinepolypropylene and I0-40 parts by weight for the butene 1-propylenecopolymer substantially having the syndiotactic structure.

For blending the substantially stereoregular crystalline polypropylenewith the butene-1-propylene copolymer substantially having thesyndiotactic structure, various conventional methods can be used.Namely, they can be mixed first in a Henschel mixer or the like and thenmelted and mixed in an extruder. As an alternative, they can be mixed ina Brabender or Banbury mixer.

The resin composition of the present invention may contain, in additionto the above polymers, one or more of known additives such asantioxidants, ultraviolet absorbers, anti-blocking agents and slipagents, depending on the end use of the composition.

The butene-1 copolymer of the present invention can also be used asformed articles such as films. The polypropylene composition of thepresent invention is useful as heat-sealing layers upon heat-bonding

Examples of the present invention will hereinafter be described. It ishowever to be noted that these examples are merely illustrative of thepresent invention and shall not be taken as limiting the presentinvention.

EXAMPLE 1

Isopropylcyclopentadienyl-1-fluorene which had been synthesized in amanner known per se in the art was converted to the lithium salt. Thelithium salt was reacted with zirconium tetrachloride, followed bypurification to obtain isopropyl(cyclopentadienyl-1-fluorenyl)zirconiumdichloride. In an autoclave having an internal capacity of 2 l, 5 mg ofthe isopropyl(cyclopentadienyl-1-fluorenyl)zirconium dichloride and 0.67g of methylaluminoxane having a polymerization degree of about 16(product of TOSOHAKZO CORPORATION) were dissolved in 1 l of toluene.Into the autoclave, 25 g of propylene were charged at 30° C., followedby the charging of 460 g of butene-1 under pressure. They werepolymerized for 1 hour. After the polymerization, unreacted monomerswere purged and 500 ml of methanol were added. The resultant mixture wasfiltered. The obtained polymer was dried at 80° C. under reducedpressure so that 44.4 g of a copolymer were obtained.

On a ¹³ C-NMR spectrum of the copolymer as measured in the form of a1,2,4-trichlorobenzene solution, the intensity of an absorption observedat about 26.9 ppm using tetramethylsilane as a standard was 0.67 of theintensity of a full absorption observed at about 27.8-26.0 ppm. Thecopolymer contained 6.0 wt.% of propylene. In addition, its intrinsicviscosity (hereinafter abbreviated as ) as measured at 135° C. in theform of a tetralin solution was 0.65. Its Mw/Mn as measured in the formof a 1,2,4-trichlorobenzene solution at 135° C. by gel permeationchromatography was 2.1.

The copolymer was press-formed at 210° C. to produce a 1 mm thick sheet.The following physical properties were then measured by thecorresponding methods which are indicated following the respectiveproperties.

Tensile yield strength, kg/cm² : ASTM D638 (23° C.)

    ______________________________________                                        Elongation, %:   ASTM D638 (23° C.)                                    Izod impact strength (notched),                                                                ASTM D256 (23° C., -10° C.)                    kg · cm/cm:                                                          Haze, %:         ASTM D1003                                                   ______________________________________                                    

The copolymer had 30 kg/cm² tensile yield strength, 47% elongation, 56and 68 kg.cm/cm Izod impact strengths (at 23° C. and -10° C.,respectively), and 30% haze.

COMPARATIVE EXAMPLE 1

Polymerization was conducted in a similar manner to Example 1 except forthe omission of propylene, so that a polymer having a syndiotacticpentad fraction of 0.89 and an Mw/Mn ratio of 1.5 was obtained. Itsphysical properties were measured in a similar manner to Example 1. Thepolymer had 108 kg/cm² tensile yield strength, 38% elongation, 48 and2.8 kg.cm/cm Izod impact strengths (at 23° C. and -10° C.,respectively), and 68% haze.

It is apparent from the foregoing results that the butene-1 copolymer ofthe present invention has greater Izod impact strength and superiortransparency compared with the homopolymer of butene-1.

Evaluation methods for the physical properties of films in the examplesand comparative examples will next be described.

Powder of each resin composition or copolymer was added with a phenolicstabilizer at a weight ratio of 20/10,000, calcium stearate at a weightratio of 5/10,000, a lubricant at a weight ratio of 9/10,000 and as ananti-blocking agent, fine powder of silicon dioxide at a weight ratio of25/10,000. They were mixed at 30°-40° C. for 4 minutes in a 20 lHenschel mixer (manufactured by Mitsui-Miike Engineering Corporation).The mass thus obtained was kneaded and pelletized by a single-screwgranulating machine having a diameter of 65 mm (manufactured by ToshibaMachine Co., Ltd.). Using a single-screw film-forming machine having adiameter of 40 mm (manufactured by Osaka Seiki K.K.), the pellets wereformed at a resin temperature of 250° C. into a film of 30 μm thick and25 cm wide by T-die extrusion. Its physical properties were evaluated.The following methods were followed to measure the respective physicalproperties.

Haze, %:

ASTM 1003-53.

Blocking tendency, %:

Two films, each 200 mm square wide, were placed in a superposed relationon an iron plate. As a weight, an iron plate of 200 mm square wide and 2kg heavy was placed over the films. After 24 hours, the percentage ofclose contact areas was calculated as the blocking tendency.

Young's modulus, kg/mm.²

Measured by an Instron-type universal tension and compression testingmachine, using films of 20 mm ×220 mm wide.

Blooming:

Visually judged after each film was held at 50° C. for 30 days.

Heat sealing temperature:

Measured by a heat-gradient testing machine manufactured by Toyo SeikiSeisaku-Sho, Ltd. Incidentally, the heat sea.ling was conducted for 1second under 2 kg/cm². The strength of heat seal of each heatsealedsample was measured by the Instron-type universal tension andcompression testing machine.

Hot tack:

A heat seal tester manufactured by Tester Sangyo K.K. was used. Thesamples were pressed for 1 second under a heat sealing pressure of 1kg/cm². The lowest temperature capable of providing a heat sealresistant to separation under a peeling load of 45 g was recorded.

Melt flow rate:

Measured at 230° C. under the load of 2.16 kg in accordance with ASTMD1238-65T.

EXAMPLE 2 Preparation of catalyst

An oscillation mill equipped with four grinding pots which had aninternal capacity of 4 l and containing 9 kg of steel balls having adiameter of 12 mm was provided. In a nitrogen gas atmosphere, 300 g ofmagnesium chloride, 115 ml of diisobutyl phthalate and 60 ml of titaniumtetrachloride were added into each pot and were ground for 40 hours.

Five grams of the above ground mixture were placed in a 200 ml flask,followed by the addition of 100 ml of toluene. The contents Were stirredat 114° C. for 30 minutes and then allowed to stand. The supernatant wasremoved. Using 100 ml of n-heptane, the solid thus obtained was washedthree times at 20° C. The solid was then dispersed in 100 ml ofn-heptane, so that a slurry of the transition metal catalyst was formed.The transition metal catalyst thus obtained contained 1.8 wt.% oftitanium and 18 wt.% of diisobutyl phthalate.

Production of propylene copolymer

As a preparatory procedure for polymerization, 25 kg of propylene and3.4 kg of butene-1 were charged in a jacketed autoclave which had aninternal capacity of 100 l and had been dried thoroughly, purged withnitrogen gas and then with propylene.

On the other hand, 500 ml of n-heptane, 4.7 ml of triethylaluminum, 2.3ml of cyclohexylmethyldimethoxysilane and 0.35 g, as solid weight, ofthe transition metal catalyst obtained above under "Preparation ofcatalyst" were mixed in a 1 l flask. The resulting mixture was chargedunder pressure into the autoclave prepared above and having the internalvolume of 100 l. After 30 g of hydrogen and 300 g of ethylene werecharged, polymerization was conducted by continuously charging propyleneat a velocity of 5 kg/hr while maintaining the internal temperature at65° C. by circulating hot water through the jacket and also charginghydrogen, ethylene and butene-1 such that their vapor-phaseconcentrations can be maintained at 2.3 mole % for hydrogen, 1.5 mole %for ethylene and 13.5 mole % for butene-1. Upon elapsed time of 3 hours,3.5 ml of diethylene glycol monoisopropyl ether were charged underpressure, followed by stirring at 60° C. for additional 30 minutes tocomplete the polymerization.

The resultant copolymer slurry was introduced at a rate of 50 kg/hrthrough a top part of a countercurrent washing column which had a thinsection having an inner diameter of 15 cm and a length of 5 m and anupper thick section having an inner diameter of 30 cm and a length of 1m. Introduced at a rate of 100 kg/hr through a bottom part was a washingliquid formed of 89 mole % of propylene, 5 mole % of propane, 1 mole %of ethylene and 15 mole % of butene-1. The washing liquid was dischargedat a rate of 110 kg/hr through the top of the column, while thethus-washed copolymer slurry was taken out at a rate of 40 kg/hr throughthe bottom of the column. Via a double-wall cylinder which had an outercylinder having an inner diameter of 20 cm and a length of 60 mm and washeated with steam circulated at 1 kg/cm² G through the outer cylinder,the copolymer slurry thus withdrawn was released into a cyclone whichwas maintained at the atmospheric pressure. The resulting powder wasdried further at 50° C. and 60 mm Hg for 10 hours, whereby 13.5 kg of acopolymer was obtained.

The copolymer had 2.1 wt.% ethylene content, 1.6 wt.% of butene content,1.63 intrinsic viscosity and 5.7 melt flow index. It was formed into afilm. The physical properties of the film were measured, indicating 2.0%haze, 10% blocking tendency, 69 kg/mm² Young's modulus, 132.8° C. heatsealing temperature, no blooming, and 142.5° C. hot tack temperature.

Production of butene-1-propylene copolymer

Isopropylcyclopentadienyl-1-fluorene which had been synthesized in amanner known per se in the art was converted to the lithium salt. Thelithium salt was reacted with zirconium tetrachloride, followed bypurification to obtain isopropyl(cyclopentadienyl-1-fluorenyl)zirconiumdichloride. In an autoclave having an internal capacity of 2 l, 5 mg ofthe isopropyl(cyclopentadienyl-1-fluorenyl)zirconium dichloride and 0.67g of methyl aluminoxane having a polymerization degree of about 16(product of TOSOHAKZO CORPORATION) were dissolved in 1 l of toluene.Into the autoclave, 30 g of propylene were charged at 30° C., followedby the charging of 460 g of butene-1 under pressure. They werepolymerized for 1 hour. After the polymerization, unreacted monomerswere purged and 500 ml of methanol were added. The resultant mixture wasfiltered. The resulting solid was dried at 80° C. under reduced pressureso that 46.8 g of a copolymer were obtained.

On a ¹³ C-NMR spectrum of the copolymer as measured in the form of a1,2,4-trichlorobenzene solution, the intensity of an absorption observedat about 26.9 ppm using tetramethylsilane as a standard was 0.67 of theintensity of an absorption observed at about 27.8-26.0 ppm. Thecopolymer contained 9.5 wt.% of propylene. In addition, its η was 0.68and its Mw/Mn was 2.1.

Preparation of resin composition

Twenty parts by weight of the above butene-1-propylene copolymer wereblended with 80 parts by weight of the above propylene copolymer. Theresultant composition was formed into a film, and physical properties ofthe film were measured. The film had 2.1% haze, 10% blocking tendency,68 kg/mm² Young's modulus, 122.6° C. heat sealing temperature, noblooming, and 128.0° C. hot tack temperature.

Comparative Example 2

A copolymer obtained by using the magnesium chloride-carried catalyst ofExample 2 and having an isotactic structure was employed as apropylene-butene-1 copolymer.

The copolymer showed almost no absorption at about 26.9 ppm and amaximum intensity (about 0.7 of an absorption intensity of the wholemethylene groups) was observed at about 27.8 ppm. The content ofpropylene units was 10.5 wt.% and η was 0.7. Evaluation was conducted ina similar manner to Example 2 except for the use of the copolymer. Thefilm had 2.2% haze, 10% blocking tendency, 63 kg/mm² Young's modulus,128.5° C. heat-sealing temperature, no blooming, and 130.0° C. hot tacktemperature. The Young's modulus was much smaller and the hot tack wassomewhat inferior.

COMPARATIVE EXAMPLE 3

In a similar manner to the preparation of the propylene copolymer inExample 2 except that the vaporphase concentration of ethylene wascontrolled at 3.6 mole %, a propylene-ethylene-butene-1 copolymercontaining 4.5 wt.% ethylene units and 1.5 wt.% butene-1 units wasobtained. The copolymer was then formed into a film as was, namely,without blending the propylenebutene-1 copolymer. The film had 1.7%haze, 10% blocking tendency, 50 kg/mm² Young's modulus, 124.6° C.heatsealing temperature, no blooming, and 135.0° C. hot tacktemperature. Similar heat sealability to the film of Example 2 wasexhibited by increasing the ethylene content. However, the Young'smodulus was significantly reduced and the hot tack was poor.

EXAMPLE 3

A butene-1-propylene copolymer having a propylene content of 17.2 wt.%was obtained in a similar manner to Example 1 except that propylene wasused in an amount of 50 g. Its η was 0.82. The intensity of anabsorption observed at about 26.9 ppm was 0.62 of the intensity of anabsorption at about 27.8-26.0 ppm. A resin composition obtained in asimilar manner to Example 1 except for the use of the copolymer wasformed into a film, and its physical properties were measured. The filmhad 2.0% haze, 15% blocking tendency, 67 kg/mm² Young's modulus, 118.5°C. heat-sealing temperature, no blooming, and 119.5° C. hot tacktemperature.

EXAMPLE 4

Using the catalyst of the same type as that employed in Example 1, 100 gof propylene, 5 g of butene-1 and 2 g of ethylene were charged underpressure into a 2 l autoclave. They were polymerized at 20° C. for 1hour. The procedure of Example 1 was thereafter followed, whereby apropylene-ethylene-butene-1 copolymer containing 1.8% of ethylene unitsand 2.5% of butene-1 units was obtained.

The η of the copolymer was 1.25, while its melt flow index was 7.2. On a¹³ C-NMR spectrum, the intensity of an absorption observed at about 20.2ppm using tetramethylsilane as a standard was at least 0.75 of theintensity of a full absorption attributed to the methyl groups ofpropylene units. The copolymer substantially had a syndiotacticstructure.

A resin composition obtained from the copolymer as in Example 2 wasformed into a film. The physical properties of the film were measured,indicating 1.5% haze, 20% blocking tendency, 48 kg/mm² Young's modulus,95° C. heat-sealing temperature, no blooming, and 98° C. hot tacktemperature.

What is claimed is:
 1. A copolymer of butene-1 and propylene, wherein,of an absorption of the side-chain methylene groups of butene-1 units ofsaid copolymer as measured in the form of a 1,2,4-trichlorobenzenesolution by ¹³ C-NMR, the intensity of an absorption observed at about26.9 ppm using tetramethylsilane as a standard is at least 0.3 of theintensity of a full absorption of the side-chain methylene groupsobserved at about 27.8-26.0 ppm using tetramethylsilane as a standard;the content of propylene units ranges from 0.1 wt.% to 20 wt.%; and theintrinsic viscosity as measured at 135° C. in the form of a tetralinsolution is at least 0.05.
 2. The copolymer of claim 1, wherein thecontent of propylene units ranges from 1 wt.% to 20 wt.%.
 3. Thecopolymer of claim 1, wherein the copolymer has a number-averagemolecular weight of at least 1,000 as measured by gel permeationchromatography in propylene.
 4. The copolymer of claim 1, wherein theratio of the weight-average molecular weight of the copolymer to thenumber-average molecular weight of the copolymer is 1.5-10.